A woman at the centre of a murder trial in Launceston has given evidence about the alleged attack.

52-year-old Michael Vernon Lowe has pleaded not guilty to the murder of his ex-girlfriend's new partner, Darren John Booth, in Kings Meadows last year.

Police allege the 37-year-old was stabbed by Lowe during a violent struggle at Crystal Wells' home.

Ms Wells told the court she saw Lowe with a knife during the fight.

The prosecution alleges Mr Booth was stabbed three times in the chest.

Ms Wells told the court she later received a phone call from Lowe and asked him how it felt to be a murderer.

She said he replied 'it felt good'.

Ms Wells testified that Lowe had previously threatened to find out where her new partner lived and hurt him.

The court also heard from 18 year old Frank Buchanan, who gave evidence about a violent struggle.

Mr Buchanan said he saw the two men fighting over a log splitter and saw a knife in Lowe's hand.

The trial continues.